function B=EMCirFuncZ(r,z,theta,r_d,z_d)

nu0 =  4*pi*10^-7;
R=sqrt(r.^2+r_d.^2-2*r.*r_d.*cos(theta)+(z-z_d).^2);
Nom=r.*(r-r_d.*cos(theta));
Denom=R.^3;
Const=nu0/(4*pi);
B=Const*Nom./Denom;
end


